The reaction of intramolecular carboxylic anhydrides with 4,5-dihydrooxazoles is a basically known chemical reaction. According to published European application 181,603, this reaction carried out, for example, in the presence of such catalysts as phosphites at a reaction temperature above 100.degree. C. gives crosslinked products which, unfortunately, are yellow to brown in color so that the systems described in this publication are largely unsuitable as paint binders.
Rowland (U.S. Pat. No. 2,543,602) described the reaction of (i) copolymers of maleic anhydride with other olefinically unsaturated monomers with (ii) bis-2,4-dihydrooxazoles, the reaction preferably taking place at temperatures above 50.degree. C.
Independent tests conducted by the present inventors have also confirmed that the reaction of maleic anhydride copolymers with 4,5-dihydrooxazoles takes place very slowly (gelation times of several days), particularly where the copolymers contain less than 25% by weight maleic anhydride. Accordingly, the known systems are unsuitable as paint binders for coating systems which require hardening in a few hours at room temperature.